Filament loading system in an extrusion apparatus

ABSTRACT

An apparatus which extrudes flowable material from a liquifier includes a system for loading filament supplied in a cassette. The cassette is loaded into a loading bay of the apparatus. A strand of filament from the cassette is engaged and advanced along a path to the liquifier using a drive wheel or roller pair. A conduit having an entrance in the loading bay guides the filament as it is advanced. The filament loading system of the present invention provides a convenient manner of loading and unloading filament in a three-dimensional modeling machine, and can be implemented in a manner that protects the filament from environmental moisture.

CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application is a continuation-in-part of application Ser.No. 09/804,401, filed on Feb. 27, 2001, which claims priority toprovisional application serial No. 60/218,642, filed Jul. 13, 2000, andwhich is also a continuation-in-part of PCT International ApplicationNo. US00/17363, filed Jun. 23, 2000 (designating the United States),which is hereby incorporated by reference as if set forth fully herein,and which is a non-provisional of provisional application serial No.60/130,165, filed Apr. 20, 1999.

BACKGROUND OF THE INVENTION

[0002] This invention relates to the fabrication of three-dimensionalobjects using extrusion-based layered manufacturing techniques. Moreparticularly, the invention relates to forming three-dimensional objectsby extruding solidifiable modeling material in a flowable state in threedimensions with respect to a base, wherein the modeling material issupplied in the form of a filament.

[0003] Three-dimensional models are used for functions includingaesthetic judgments, proofing the mathematical CAD model, forming hardtooling, studying interference and space allocation, and testingfunctionality. Extrusion-based layered manufacturing machines build upthree-dimensional models by extruding solidifiable modeling materialfrom an extrusion head in a predetermined pattern, based upon designdata provided from a computer aided design (CAD) system. A feedstock ofeither a liquid or solid modeling material is supplied to the extrusionhead. One technique is to supply modeling material in the form of afilament strand. Where the feedstock of modeling material is in solidform, a liquifier brings the feedstock to a flowable temperature fordeposition.

[0004] Examples of extrusion-based apparatus and methods for makingthree-dimensional objects are described in Valavaara U.S. Pat. No.4,749,347, Crump U.S. Pat. No. 5,121,329, Crump U.S. Pat. No. 5,340,433,Crump et al. U.S. Pat. No. 5,503,785, Danforth, et al. U.S. Pat. No.5,900,207, Batchelder, et al. U.S. Pat. No. 5,764,521, Dahlin, et al.U.S. Pat. No. 6,022,207, Stuffle et al. U.S. Pat. No. 6,067,480 andBatchelder, et al. U.S. Pat. No. 6,085,957, all of which are assigned toStratasys, Inc., the assignee of the present invention.

[0005] In the modeling machines employing a filament feed, modelingmaterial is loaded into the machine as a flexible filament wound on asupply reel, such as disclosed in U.S. Pat. No. 5,121,329. Asolidifiable material which adheres to the previous layer with anadequate bond upon solidification and which can be supplied as aflexible filament is used as the modeling material. The extrusion head,which includes a liquifier and a dispensing nozzle, receives thefilament, melts the filament in the liquifier, and extrudes moltenmodeling material from the nozzle onto a base contained within a buildenvelope. The modeling material is extruded layer-by-layer in areasdefined from the CAD model. The material being extruded fuses topreviously deposited material and solidifies to form a three-dimensionalobject resembling the CAD model. In building a model from a modelingmaterial that thermally solidifies upon a drop in temperature, the buildenvelope is preferably a chamber which is heated to a temperature higherthan the solidification temperature of the modeling material duringdeposition, and then gradually cooled to relieve stresses from thematerial. As disclosed in U.S. Pat. No. 5,866,058, this approach annealsstresses out of the model while is being built so that the finishedmodel is stress free and has very little distortion.

[0006] In creating three-dimensional objects by depositing layers ofsolidifiable material, supporting layers or structures are builtunderneath overhanging portions or in cavities of objects underconstruction, which are not supported by the modeling material itself.For example, if the object is a model of the interior of a subterraneancave and the cave prototype is constructed from the floor towards theceiling, then a stalactite will require a temporary support until theceiling is completed. A support structure may be built utilizing thesame deposition techniques and apparatus by which the modeling materialis deposited. The apparatus, under appropriate software control,produces additional geometry acting as a support structure for theoverhanging or free-space segments of the object being formed. Supportmaterial is deposited either from a separate dispensing head within themodeling apparatus, or by the same dispensing head that depositsmodeling material. A support material is chosen that will adhere to themodeling material during construction, and that is removable from acompleted object. Various combinations of modeling and support materialsare known, such as are disclosed in U.S. Pat. No. 5,503,785.

[0007] In Stratasys FDM® three-dimensional modeling machines of thecurrent art which embody a filament feed as disclosed in theabove-referenced patents, a coil of modeling filament wrapped on a spoolis loaded into the machine by mounting the spool onto a spindle. Thefilament is made of a thermoplastic or wax material. The user manuallyfeeds a strand of the filament through a guide tube made of low frictionmaterial, unwinding filament from the spool until the filament strandreaches a pair of motor-driven feed rollers at the extrusion head. Thefilament strand is advanced by the feed rollers into a liquifier carriedby the extrusion head. Inside the liquifier, the filament is heated to aflowable temperature. As the feed rollers continue to advance filamentinto the extrusion head, the force of the incoming filament strandextrudes the flowable material out from the dispensing nozzle where itis deposited onto a substrate removably mounted to a build platform. Theflow rate of the material extruded from the nozzle is a function of therate at which the filament is advanced to the head and the size of thedispensing nozzle orifice. A controller controls movement of theextrusion head in a horizontal x, y plane, controls movement of thebuild platform in a vertical z-direction, and controls the rate at whichthe feed rollers advance filament into the head. By controlling theseprocessing variables in synchrony, the modeling material is deposited ata desired flow rate in “beads” or “roads” layer-by-layer in areasdefined from the CAD model. The dispensed modeling material solidifiesupon cooling, to create a three-dimensional solid object.

[0008] The Stratasys FDM® modeling machines use modeling filaments whichare made from moisture sensitive materials, e.g., ABS thermoplastic. Inorder for the machines to function properly and to build accurate,robust models, the material must be kept dry. Therefore, filament spoolsfor use in the machines are shipped, together with packets of desiccant,in moisture-impermeable packages. Each filament spool is to remain inits package until it is loaded into a modeling machine. The spindle ontowhich the spool is mounted is contained in a “drybox”, an area of themachine maintained at low humidity conditions. The user is instructed toplace the desiccant packets packaged with the filament spool into thedrybox, and to remove any desiccant packets placed in the machine withprior spools. After manually feeding the filament to the feed rollers,the user latches a door of the drybox and may instruct the machine tobegin building a model. To unload the filament spool from the machine,the user manually winds the filament back onto the spool. U.S. Pat. No.6,022,207 shows and describes a spool of the current art loaded into thedrybox of a three-dimensional modeling machine.

[0009] Manually feeding filament to the head, as is presently done, canbe tedious. Additionally, as a practical matter, users often leave olddesiccant in the drybox and fail to replace it with new desiccant,allowing humidity in the drybox to reach unacceptable levels. Further,frequent switching of spools results in moisture-contaminated material.Opening and closing the drybox door allows humid air to get trappedinside of the sealed area. A partially used spool unloaded from themachine is exposed to moisture and becomes contaminated as well. Thesemoisture contamination problems result in wasted material when the userswitches the type or color of modeling material. Moreover, somematerials desirable for use as modeling materials in the Stratasys FDM®machines are highly vulnerable to moisture and can get contaminatedwithin minutes. The time during which the drybox door is opened forloading and unloading filament introduces a level of moisture into thedrybox unacceptable for some desirable materials, limiting the choice ofmodeling materials for use in these machines.

[0010] It would be desirable to provide modeling filament to athree-dimensional modeling machine in a manner that would simplify theloading and unloading operation, and that would reduce the moistureintroduced into the machine. Additionally, it would be desirable to beable to readily remove unused filament from the machine and store it forlater use.

BRIEF SUMMARY OF THE INVENTION

[0011] The present invention is an extrusion apparatus which includes asystem for loading filament supplied in a cassette. The extrusionapparatus, such as a three-dimensional deposition modeling machine, hasa liquifier that receives a feedstock of material in filament form anddelivers the material in a flowable state. The apparatus includes aloading bay which receives the filament cassette and means for advancinga strand of the filament from the cassette towards the liquifier. In theexemplary embodiments, a conduit is provided for guiding the filamentstrand along the path towards the liquifier. Optionally, an entrance ofthe conduit makes an airtight seal with an exit orifice of the cassette,and the filament is protected from environmental moisture as it isadvanced to the liquifier.

[0012] An extrusion apparatus may include multiple loading bays, eachreceiving a filament cassette. In the exemplary embodiments, a latchingmeans engages and disengages the filament cassette in the loading bayand a registration means aligns the exit orifice of the cassette withthe entrance of the conduit. The filament loading system of the presentinvention provides a convenient manner of loading and unloading filamentin a three-dimensional modeling machine.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a perspective, diagrammatic view of a genericfilament-feed used in an extrusion-based three-dimensional modelingmachine.

[0014]FIG. 2 shows a first embodiment of a filament cassette beingloaded into a first embodiment of a three-dimensional modeling machine.

[0015]FIG. 3 is a partially exploded view of the first embodiment of afilament cassette.

[0016]FIG. 4 is an exploded view of the spool and lower shell of thefilament cassette shown in FIG. 3.

[0017]FIG. 5 is a detailed view of the (partially) exploded filamentcassette shown in FIG. 3, showing a strand of filament in the filamentpath and a mounted circuit board.

[0018]FIG. 5A is a detailed view of an alternative configuration of acircuit board mounted onto the first embodiment of a filament cassette.

[0019]FIG. 6 is a perspective view of the first embodiment of thefilament cassette, showing the bottom surface, side and trailing edge ofthe cassette.

[0020]FIG. 7 is a front elevation of the first embodiment of thefilament cassette.

[0021]FIG. 8 is top plan view of a first embodiment of a filamentcassette receiver of the present invention.

[0022]FIG. 9 is a front elevation of the first embodiment of thefilament cassette receiver.

[0023]FIG. 10 is a perspective, detailed view of the filament driveshown in FIG. 8 as part of the filament cassette receiver.

[0024]FIG. 11A is a top plan view of the first embodiment of a filamentcassette loaded into the filament cassette receiver of FIG. 8, showingthe filament drive assembly in a disengaged position.

[0025]FIG. 11B is a top plan view of a filament cassette loaded into thecassette receiver of FIG. 6, showing the filament drive assembly in anengaged position.

[0026]FIG. 12 is a perspective detailed view of the filament driveassembly of FIG. 11B engaging a roller on the first embodiment of thefilament cassette.

[0027]FIG. 13 is a perspective view of a filament loading assembly in asecond embodiment of the three-dimensional modeling machine.

[0028]FIG. 14 is a perspective view of a second embodiment of thefilament cassette.

[0029]FIG. 15 is an exploded view of the second embodiment of thefilament cassette (guide block not shown).

[0030]FIG. 16 is a perspective view of the canister base of the secondembodiment of the filament cassette.

[0031]FIG. 17 is a perspective view of the guide block shown in FIG. 14,with the access door open.

[0032]FIG. 18 is an exploded view of the filament cassette receivershown in FIG. 13.

[0033]FIG. 19 is a sectional view of the filament loading assembly ofFIG. 13, taken along a line 19-19 thereof.

DETAILED DESCRIPTION

[0034] A filament feed 10 used generally to feed filament to anextrusion head 20 in an extrusion-based three-dimensional modelingmachine is shown in FIG. 1. A spool 12 carrying a coil of filament 14 ismounted on a spindle 16. The filament 14 is made up of a modelingmaterial from which a three-dimensional model (or a support structurefor the three-dimensional model) is to be built. Typically, the filamenthas a small diameter, such as on the order of 0.070 inches.

[0035] A strand of the filament 14 is fed through a guide tube or tubes18, made of a low-friction material, which also preferably provides amoisture barrier, such as Teflon™. The, guide tube 18 routes the strandof filament 14 to the extrusion head 20. A pair of feed rollers 22,shown mounted on the extrusion head 20, receive the strand of filament14 and feed the strand of filament 14 to a liquifier 26 carried by theextrusion head 20. As shown, the feed rollers 22 are rubber-coated so asto grab the strand of filament 14 therebetween. Also as shown, one offeed rollers 22 is a drive roller, driven by a motor 24 under thecontrol of a controller 25. The other roller 22 is an idler roller. Theliquifier 26 is heated so as to melt the filament 14. The liquifier 26terminates in a nozzle 28 having a discharge orifice 30 for dispensingthe molten modeling material. The liquifier 26 is pressurized by the“pumping” of the strand of filament 14 into the liquifier 26 by feedrollers 22. The strand of filament itself acts as a piston, creating a“liquifier pump”. The pressurization impels the molten modeling materialout of the orifice 30 at a volumetric flow rate. The volumetric flowrate is a function of the size of the dispensing orifice 30 and the rateof rotation of the feed rollers 22. By selective control of the motor24, the rate of advancement of the strand of filament 14, and thus thevolumetric dispensing rate of the molten modeling material, can beclosely controlled.

[0036] The extrusion head 20 is driven in a horizontal x,y plane by anx-y translator 34, which receives drive signals from the controller 25in accordance with design data derived from a CAD model. As theextrusion head 20 is translated in the x-y plane, molten modelingmaterial is controllably dispensed from the orifice 30 layer-by-layeronto a planar base 32 (shown in part in FIG. 1). After each layer isdispensed, the base 32 is lowered a predetermined increment along avertical z-axis by a z-axis translator 36, which also receives drivesignals from the controller 25. The dispensed material fuses andsolidifies to form a three-dimensional object resembling the CAD model.Support material may be dispensed in a like fashion in coordination withthe dispensing of modeling material, to build up supporting layers or asupport structure for the object.

[0037] As will be understood by those in the art, many variations of themodeling machine and process are possible. For example, any relativemovement in three-dimensions between the extrusion head 20 and the base32 may be used to built up the object. The feed rollers and the motormay take various forms. For example, as is disclosed in U.S. Pat. No.5,121,329, both rollers may be driven (such as by coupling the rollersby a timing belt), more rollers be added, or the rollers may bespring-biased towards each other, rather than rubber coated, to maintaingripping frictional contact on the filament. Any type of motor that candrive the feed rollers at a controlled rate may be employed, forinstance a servo motor or a stepper motor. Likewise, differentarrangements of extrusion heads may be utilized for receiving anddispensing different types or colors of filament from separate filamentfeeds. For example, the extrusion head may carry two sets of feedrollers, each driven by its own motor, for advancing two differentfilament strands from two different spools, such is disclosed in U.S.Pat. Nos. 5,121,329; 5,503,785; and 6,004,124.

EMBODIMENT ONE

[0038] In the present invention, the spool carrying a coil of filamentis contained within a filament cassette. FIG. 2 shows a first exemplaryembodiment of a modeling machine 40 which has two loading bays 42stacked vertically, each for receiving a first embodiment of a filamentcassette 44. As shown, one filament cassette 44 is loaded into the lowerloading bay. A second cassette 44 is being loaded into the upper loadingbay 42. Each filament cassette contains a spool carrying a coil offilament. Preferably, one cassette 44 supplies filament formed ofmodeling material, while the other cassette 44 supplies filament formedof support material. The modeling machine 40 has two liquifiers 26, suchas shown in FIG. 1, which each receive a strand of filament from one ofthe cassettes 44.

[0039] As will be described in detail below, each loading bay 42contains a cassette receiver 46 which engages the filament cassette 44and advances a strand of the filament 14 from the cassette 44 into theguide tube 18 of filament feed 10. A user loads the filament cassette 44into the modeling machine 40 by holding the cassette 44 in an uprightposition and lining up a leading edge 48 of the cassette 44 with one ofthe loading bays 42. The user pushes the cassette 44 into the loadingbay 42 until a hard stop is reached. At such time, the cassette 44 isengaged by the cassette receiver 46.

[0040] Detail of the filament cassette 44 is shown in FIGS. 3-7. Asshown in FIGS. 3 and 4, the filament cassette 44 is comprised of anupper shell 50, a lower shell 52, and a spool 54 carrying the filament14. The upper shell 50 and lower shell 52 fasten together, with thespool 54 between them, by a set of four screws 55 (not shown). The lowershell 52 has a hub 56 and the upper shell 50 has a hub 58. A circularrecess 59 within upper shell 50 and lower shell 52 surrounds each ofhubs 56 and 58. The upper shell 50 and lower shell 52 each have sevencompartments 60 along the periphery of the recess 59. Together, hubs 56and 58 form a spindle on which the spool 54 rotates within a chamberdefined by the circular recesses 59. Packets of desiccant 62 are placedin the compartments 60 so as to maintain dry conditions in the chamberof cassette 44. A narrow channel 64 is routed in lower shell 52 in aclosed-loop around the periphery of the circular recesses 59 and thecompartments 60. A gasket 68 is seated in the channel 64, and a ridge 66in the upper shell 50 mirrors the channel 64. The gasket 68 blocks airfrom reaching the spool 54 within the cassette 44 when the upper shell50 and the lower shell 52 are fastened together.

[0041] Each of shells 50 and 52 have a narrow channel 70 leading fromthe circular recess 59 to the leading edge 48 of the cassette 44, asbest shown in FIG. 5. Together, the channels 70 define a filament pathwhich terminates in an exit orifice 72 of the cassette 44, as shown inFIG. 7. As is best shown in FIG. 5, a roller 76 is mounted opposite aroller 78 along the channel 70 of the lower shell 52. As shown, roller76 rotates on a floating axle 80, while roller 78 rotates on a fixedaxle 82. The floating axle 80 is seated in an oblong depression 81 ofthe upper and lower shells 50 and 52, oriented perpendicular to thefilament path. The fixed axle 82 is seated in a cylindrical depression83 of the upper and lower shells 50 and 52. A force applied againstroller 76 will force roller 76 towards roller 78 to grip a strand offilament 14 in the filament path. Alternatively, both rollers could havea fixed axle, and be positioned close enough to one another to grip afilament strand in the path. The rollers may have an elastomericsurface, to aid in gripping the strand of filament 14.

[0042] The channel 70 of lower shell 52 forming the filament pathcrosses the channel 64 at a position located between the circular recess59 and the roller pair 76 and 78. A retainer 84, which is integral withthe gasket 68, is positioned at this location. The retainer 84 has acenter hole 85 of a diameter approximately equal to the filamentdiameter.

[0043] Each of shells 50 and 52 have another channel 86 which runsparallel to the channel 70. Together, the channels 86 define aregistration pin receiving cavity 88, which begins at the leading edge48 of the cassette 44 and terminates before reaching the gasket 68.Cavity 88 has a flared mouth followed by a narrow neck. The mouth ofcavity 88 is shown in FIG. 7. Each of upper shell 50 and lower shell 52have a recess 89 to the right of the channel 86, which together form arecess in the leading edge 48 of the cassette 44. On the lower shell 52,a circuit board is mounted in the recess 89.

[0044] In one embodiment, as shown in FIG. 5, a circuit board 92 ismounted horizontally at the base of the recess 89 by two screws 94, andcarries an EEPROM 96 on its upper surface. The circuit board 92 hasconductive tabs 98 on a portion thereof which extends across the recess89, so that it may be received by a card-edge connector. In analternative embodiment, shown in FIG. 5A, a circuit board 102 is mountedvertically in the recess 89 by screws 104. The circuit board 102 has aninner face (not shown) which carries the EEPROM 96 and an outer facewhich carries a pair of electrical contacts 106.

[0045] The EEPROM 96 acts as an electronic tag for the cassette 44. TheEEPROM 96 contains information identifying the cassette 44 and thefilament 14, such as the type of material from which the filament isformed. The EEPROM 96 additionally may keep a count of the lineal feetof filament 14 that is in the cassette 44. When the cassette 44 isloaded into the modeling machine 40, the EEPROM 96 is electricallyconnected to the controller 25, as described below. As filament 14 isadvanced from the cassette 44 into the modeling machine 40, thecontroller 25 continually updates the lineal feet count of the filament14 remaining in the cassette 44. This allows the controller. 25 toprevent the machine 40 from attempting to model without filament. EEPROM96 may be any electronically readable and writeable data store. The useof such a data store as a filament tag is described in U.S. Pat. No.5,939,008.

[0046] The filament cassette 44 is assembled by placing the spool 54carrying the filament 14 on the hub 56 of the lower shell 52. The lowershell 52 is prepared by pressing the gasket 68 into the channel 64, sothat the center hole 85 of the retainer is aligned in the channel 70.One of the circuit boards 92 or 102 is fastened to the lower shell 52.The fixed axle 82 carrying roller 78 is placed into the cylindricaldepression 82 of the lower shell 52, while the floating axle 80 carryingroller 76 is placed into the oblong depression 81 of the lower shell 52.A strand of the filament 14 from the spool 54 is threaded through thehole in retainer 84, and placed in the channel 70 of lower shell 52between the rollers 76 and 78. A packet of desiccant is placed in eachof the compartments 60. Once each of these items are in position on thelower shell 52, the upper shell 50 and lower shell 52 are fastenedtogether by the four screws 55 (alternatively, any known fasteningdevice could be used). The screws 55 are set into four screw holes 108of the lower shell 52, and extend into four threaded screw holes 109 ofthe upper shell 50. The cassette 44 is then ready for loading into themodeling machine 40.

[0047] Once the cassette 44 is assembled, it may be placed in amoisture-impermeable package, which package may then be vacuum sealed,for shipping or later use. Vacuum sealing is desirable where thefilament 14 is made from a moisture sensitive material. Additionally,for moisture sensitive materials, the chamber of the cassette 44containing the spooled filament should be dried just prior to the vacuumsealing. The cassette 44 then remains in the package until a user isready to load the cassette 44 into the modeling machine 40.

[0048] After the filament 14 contained within the cassette 44 isdepleted or otherwise becomes unusable, the cassette 44 can be refilledand reused by detaching the shells 50 and 52 and replacing the filament14 on the spool 54. The EEPROM 96 carried by circuit board 92 or 102 canbe reset or the circuit board replaced to provide a new EEPROM 96.

[0049]FIG. 6 shows the bottom surface, trailing edge and right side offilament cassette 44. As shown, the roller 76 protrudes from an opening111 in the right side of the cassette 44 so that it may receive anexternal rotational force. As will be described in more detail below,the roller 76 is preferably driven by a drive wheel 156 on the cassettereceiver 46 to advance the strand of filament 14 out of the exit orifice72.

[0050] The cassette receiver 46 which engages filament cassette 44 isshown in FIGS. 8-12. The cassette receiver 46 is mounted on the floor110 of each loading bay 42. Preferably, the loading bay floor 110 ismade of sheet metal. The cassette receiver 46 comprises a latchingmechanism 112, a reciprocating assembly 114 and a drive assembly 116.The latching mechanism 112 is mounted to the floor 110 by a bracket 116.The latching mechanism 112 is comprised of a solenoid 118, an arm 120and a latch 122. The arm 120 is coupled to the solenoid 118 at one endthereof and is integral with the latch 122 at the other end thereof. Thearm 120 extends downward from the solenoid 118 through an opening in thefloor 110, sits below and generally parallel to the floor 110, and thenangles upward so that it will pivot to position the latch 122alternately above and below the floor 110. The latch 122 moves up anddown through a cutout 124 in the floor 110.

[0051] The solenoid 118, operating under control of the controller 25,alternately rocks the arm 120 up and down to engage and disengage thelatch 122. When the solenoid 118 is energized, the arm 120 rocks upwardat the latch end, placing the latch 122 in an engaged position. When thesolenoid 118 is de-energized, the latch end of arm 120 rocks downward,moving the latch 122 to a disengaged position.

[0052] The reciprocating assembly 114 is fastened to the loading bayfloor 110 by a bracket 126. The reciprocating assembly 114 comprises apiston 128, an ejection spring 130, a track 132 and a frame 133. Thepiston 128 sits parallel to and above the floor 110. The piston 128extends through a hole in the bracket 126 and moves forward and back inthe loading bay 42, guided by track 132. The forward end of the piston128 is coupled to the frame 133, which extends generally perpendicularto the piston 128. The frame 133 moves back and forth with the motion ofpiston 128. The ejection spring 130 is coiled around the piston 128,connecting to the bracket 126 at the rearward end thereof and connectingto the frame 133 at the forward end thereof. A horizontal force appliedagainst the frame 133 will compress the ejection spring 130. When saidforce is released, the spring 130 will decompress, causing the frame 133and piston 128 to move forward. A pair of bearings 134 are mounted tothe floor 110 underneath the frame 133. The bearings 134 provide a lowfriction surface which supports frame 133 in a plane parallel to thefloor 110, while allowing the frame 133 to slide back and forth.

[0053] Attached to the frame 133 are an electrical connector 136, aregistration pin 138 and a conduit 140. The electrical connector 136 isconfigured to mate with the circuit board of the filament cassette 44 ona forward face thereof and is configured to provide an electricalconnection to the controller 25 at a rear face thereof. As shown, theforward face of electrical connector 136 carries two pogo pins 142configured to mate with the electrical contacts 106 of circuit board 102carried by the cassette 44. (Alternatively, the electrical connectorcould be a card-edge connector for receiving the conductive tabs 98 ofcircuit board 92). The registration pin 138 is mounted on the frame 133to the right of the electrical connector 136. The registration pin 138extends forward in the loading bay 42 and has a diameter approximatelyequal to the diameter of the neck of cavity 88 within the filamentcassette 44. The conduit 140 is located to the right of the registrationpin 138. The conduit 140 has an entrance 144 which faces forward in theloading bay 42, and an exit 146 facing to the rear of the loading bay42. The entrance 144 of the conduit 140 is configured to align with theexit orifice 72 of the cassette 44, and to receive the strand offilament 14 from the exit orifice 72. Optionally, the conduit 140 maymake an airtight seal with the exit orifice 72 and the guide tube 18. Astrand of the filament 14 fed into the conduit entrance 144 will exitthrough the conduit exit 146 where it can then be provided into theguide tube 18 and routed to the liquifier 26.

[0054] The drive assembly 116 is mounted to the loading bay floor 110 bya bracket 148. The drive assembly 116 comprises a solenoid 150, a motor152, a gear train 154, a drive wheel 156 which rotates on a shaft 158,and a housing 160. The drive assembly 116 is shown in detail in FIGS.10-12. The solenoid 150 having an actuator 162 is mounted in the bracket148 so that the actuator 162 reciprocates forward and back in theloading bay 42. Energization of the solenoid 150 is controlled by thecontroller 25. The actuator 162 moves forward in the loading bay 42 whenthe solenoid 150 is actuated, and moves towards the back of the loadingbay 42 when the solenoid 150 is deactuated. The housing 160, whichcarries the motor 152, the gear train 154 and the drive wheel 156, ispivotably mounted onto the floor 110 in front of the actuator 162. Whenthe solenoid 150 is energized, the actuator 162 pivots the housing 160in a clockwise rotation. Absent a force imparted against the housing 116by the actuator 162, the housing 160 is in an upward resting position.When the actuator 162 rotates the housing 116 in a counterclockwisedirection, the drive wheel 156 is placed in an actuated position atwhich it will press against the floating-axis roller 76 of the cassette44 when the cassette 44 is loaded in the loading bay 42.

[0055] The motor 152, in response to control signals from the controller25, causes rotation of the shaft 158 via gear train 154, as best shownin FIG. 10. Rotation of the shaft 158 rotates the drive wheel 156. Whenin its actuated position, the drive wheel 156 will then rotate thecassette roller 76. Release of the actuator 162 from the housing 160allows the housing 160 to rotate back into a resting position. In analternative embodiment wherein the cassette roller has a fixed axis, thesolenoid 150 could be eliminated and the drive wheel 156 could remainfixed in the actuated position where it would impart a constant forceagainst the cassette roller.

[0056] As mentioned above, a user loads the cassette 44 into themodeling machine 40 by pushing the cassette 44 into one of the loadingbays 42 until a hard stop is reached. The hard stop is provided by abackstop 164, which is mounted to the loading bay floor 110 (as shown inFIG. 8), and the compression of the ejection spring 130. As the userreleases the cassette 44, it moves back until the latch 122 catches on aridge 180 on the bottom surface of the cassette 44 (shown in FIG. 6).The latch 122 is set in an upward position prior to loading the cassette44, under commands from the controller 25 to the solenoid 118, so thatit is ready to catch the cassette 44. The latch 122 remains in thisupward position until the user desires to remove the cassette 44, atwhich time the controller 25 de-energizes the solenoid 118 to lower thelatch 122.

[0057] As the cassette 44 is pushed into the loading bay 42, theregistration pin 138 slides into the cavity 88 of the cassette 44. Theregistration pin 138 serves to properly align the cassette 44 with thecassette receiver 46, and specifically to counteract a torque impartedagainst the cassette 44 by engagement of the drive system 116. With thecassette 44 properly aligned with the cassette receiver 46, the pogopins 142 mate with the electrical contacts 106 of the circuit board 102.Electrical contact is then established between the cassette 44 and thecontroller 25. The controller 25 knows that the cassette 44 is loadedwhen it senses that the EEPROM 96 is present. The controller 25 readsthe count that is stored on the EEPROM 96. If the count indicates thatthe amount of filament 14 contained in the cassette 44 is below a set“cassette empty” threshold value, the user is alerted to load a newcassette 44.

[0058] When the controller 25 senses that the cassette 44 is loaded, itenergizes the solenoid 150 of the drive assembly 116. As describedabove, actuation of the solenoid 150 rotates the housing 160 such thatthe drive wheel 156 moves to its actuated position, at which it pressesagainst the roller 76 of the cassette 44. The drive wheel 156 imparts aforce against the roller 76, pushing the roller 76 towards the roller78, thus pinching the strand of filament 14 that is in the filamentpath. When the drive wheel 156 is driven in a counterclockwise rotationby the motor 152, the roller 76 is driven in a clockwise-rotation so asto advance the strand of filament 14 into the conduit 140, and then intothe guide tube 18.

[0059] The cassette receiver 46 continues to advance the strand offilament 14 until it reaches the feed rollers 22. The controller 25senses presence of the filament 14 at the feed rollers 22. Preferably,motor 24 is a DC servo motor, and the sensing is achieved by monitoringthe current load of the motor 24. To monitor the current load, thecontroller 25 activates the motor 24 at the start of the auto-loadprocess. When filament is present between the rollers 22, the currentload will increase. When the controller 25 senses the increase in motorcurrent load, the controller 25 signals the motor 24 and the cassettereceiver 46 to stop. Additionally, the controller 25 de-energizes thesolenoid 150 to remove the force of drive wheel 156 against the roller76. This serves to remove the frictional force of the rollers from thefilament 14 during modeling. Filament 14 from each of the cassettes 44is loaded in a like manner. Once both materials have been loaded,modeling may begin.

[0060] Optionally, as mentioned above, the drive assembly 116 could bedesigned so that the drive wheel 156 remains in a fixed position whereit applies a constant force. In such an arrangement, it would bepossible to eliminate the roller pair 22, and instead use the rollerpair on the cassette 44 to feed the filament 14 into the liquifier 26.Then, the drive wheel 156 would be driven at a controlled rate tocontrol the rate of advancement of the filament 14 into the liquifier26.

[0061] To unload the filament, a controller 25 drives the motor 24backwards for a short time sufficient to pull the strand of filament 14out of the liquifier 26 and feed rollers 22. The controller 25 thendisengages the cassette receiver 46 from the cassette 44, allowing theuser to remove the cassette 44 from the loading bay 42. To eject thecassette 44 from the machine 40, the user pushes the cassette 44 to thehardstop to allow disengagement of the latch 122. The spring 130 thenforces forward the reciprocating assembly 114, ejecting the cassette 44.

[0062] The top surface and trailing edge of cassette 44 each have awindow 170 which allow the user to visually inspect the amount offilament 14 contained within the cassette 44 when the cassette 44 isloaded or unloaded. If a useable amount of filament 14 remains in thecassette 44 when it is removed from the loading bay 42, the cassette canbe stored for later use. If there is not a usable amount of filamentremaining, the cassette 44 can be refilled and reused.

EMBODIMENT TWO

[0063]FIG. 13 shows a filament loading assembly 178 in a secondembodiment of a modeling machine 180, which builds models from filamentsupplied from a second exemplary embodiment of a filament cassette 184.The filament loading assembly 178 and the filament cassette 184 areparticularly suited for building models from moisture-sensitivematerials. The filament loading assembly 178 comprises four loading bays182, four filament cassettes 184 each containing a spool 186 carrying acoil of filament 188, four filament cassette receivers 190, two junctionblocks 192 and a drying system 194. The four loading bays 182 arealigned horizontally across the front of the modeling machine 180. Eachloading bay 182 receives one filament cassette 184 and has associatedwith it one filament cassette receiver 190, mounted in a ceilingthereof. The junction blocks 192 are mounted to a frame 195 of thefilament loading assembly 178, and are each associated with a pair ofcassette receivers 190.

[0064] A user loads the filament cassette 184 into the modeling machine180 by holding the cassette 184 in an upright position, pushing thecassette 184 into one of the loading bays 182, grasping a latch 196 onthe filament cassette receiver 190, and pulling the latch 196 forward todrop the filament cassette receiver 190 to a lowered position. In thelowered position, the filament cassette receiver 190 mates with thefilament cassette 184 and latches the cassette 184 into place. A strandof filament is manually fed from each filament cassette 184 to theassociated cassette receiver 190 (as will be described in detail below).The cassette receiver 190, under control of the controller 25, thenautomatically advances the filament strand through tubing 202 and theassociated junction block 192 toward the extrusion head 20.

[0065] Each junction block 192 has two input ports 198, one air port199, and one output port 200. The input ports 198 are coupled to theassociated cassette receivers 190 by lengths of tubing 202, whichprovides a path for filament strands from the receivers 190 to theassociated junction block 192. The output ports 200 of each junctionblock 192 are connected to lengths of tubing 204. Tubing 204 provides afilament path from each junction block 192 to a liquifier 26 (such asshown in FIG. 1). For filament 188 that is made of a moisture sensitivematerial, the drying system 194, which comprises a compressor 206, afilter 208, and a regenerative dryer 210, is used to maintain dryconditions in the path of the filament strand as it travels from thecassette 184 to the liquifier 26, as will be described in more detailbelow.

[0066] At a given time, only one strand of filament is provided to eachjunction block 192 and to each pair of feed rollers 22. The otherfilament strands remain in the associated cassette receivers 190. Acassette 184 that provides the filament strand to the junction box 192is termed a primary material supply cassette, while a cassette 184 whichprovides the filament strand that remains in the cassette receiver 190is termed a standby material supply-cassette. The machine 180 can switchfrom the primary to the standby material supply cassette 184 withoutuser intervention, by winding the filament strand from the primarycassette 184 back towards its receiver 190, and advancing the filamentstrand from the standby cassette 184 through the junction block 192 tothe feed rollers 22. The standby cassette then becomes the primarycassette. In a typical modeling application, it will be preferable forone junction block 192 to receive modeling material filament and theother junction block 192 to receive support material filament. Then, themachine 180 can automatically switch to the standby supply when theprimary supply is depleted, and no modeling time will be lost. Thedepleted cassette can be replaced at the user's convenience while themodeling machine 180 continues to run. Alternatively, if the primary andstandby cassettes 184 contain different types of filament 188, switchingcan be done before depletion of material to allow building from adifferent material type or color.

[0067] The filament cassette 184 is shown in detail in FIGS. 14-17. Asshown, the filament cassette 184 is comprised of a canister 212, a guideblock 214, and spool 186 carrying a coil of the filament 188. Thecanister 212 is formed of a body 216, and a lid 218 that presses ontothe body 216. The interior of canister 212 defines a chamber containingthe spool 186. The spool 186 rotates on a hub 220 of the body 216 and ahub 221 of the lid 218. Optionally, a spring plate 222 is attached tothe inside of the lid 218. The spring plate 222 has spiked fingers whichare bent so as to allow rotation of the spool 186 in only the directionthat will advance filament out of the cassette 184. The guide block 214is attached to the body 216 at an outlet 224, and provides a exit pathfor the filament 188. The guide block 214 is fastened to the canisterbody 216 by a set of screws (not shown) which extend through six screwholes 232 in the body 216 (shown in FIG. 15).

[0068] For filament 188 made of moisture sensitive material, thecassette 184 is made air tight. The canister 212 and guide block 214 aremade of materials that block water vapor transmission, such as sheetmetal and polypropylene, respectively. A strip of moisture-impermeabletape 223 seals the lid 218 to the body 216. Moisture can be withdrawnfrom the interior chamber of canister 212 through a hole 226 in thecanister body 216, and the hole 226 sealed with a plug 228. Preferably,a piece of moisture-impermeable tape 230 is placed over the plug 228 tofurther seal the hole 226.

[0069] As shown in FIG. 19, a strand of the filament 188 inside thecanister 212 is fed through outlet 224 into a filament path 236 in theguide block 214. The filament path 236 extends through the guide block214, terminating in an exit orifice 238. Adjoining the filament path236, the guide block 214 has a chamber 238 in which a knurled roller 240is mounted on a pin 242. The pin 242 is mounted so that the knurledroller 240 pinches the strand of filament in the path 236 against a wall246. A user can advance the filament strand out of the exit orifice 238and along the filament path 236 by manually rotating the roller 240 in aclockwise direction. To prevent a counterclockwise rotation of roller240 (which would push the filament strand towards the canister 212 whereit could be accessed only by opening the canister), an anti-rotationplate 244 is preferably mounted in the chamber 238, juxtaposed with theroller 240. It will be apparent to those skilled in the art that theknurled roller 240 could be replaced with some other means for advancingthe filament strand. For example, the wall 246 could have a raisedcontour allowing a user to apply a manual propulsion force to thefilament over the contour. Further, the raised counter could be definedby an idler rollers or an idler roller could be used in combination withthe knurled roller 240.

[0070] For filament 188 formed of moisture sensitive material, air flowto the filament path 236 is prevented. The guide block 214 has aremovable plug cap 248 that seals the exit orifice 238, and a door 250that encloses the chamber 238. The plug cap 248 snap-fits onto a pair ofgrooves 254 on the guide block 214, so that a compressible seal 252 onthe underside of the plug cap 248 covers the exit orifice 238. The plugcap 248 is removed by the user at the time of inserting the cassette 184into the machine 180. Preferably, the guide block has a second set ofgrooves 256 on which the plug cap 248 may be parked when it is removedfrom the first set of grooves 254. The door 250 has a compressible seal258 on an interior surface thereof, and pivots on a hinge 260. When thedoor 250 is open, the roller 240 is accessible to a user. The door 250is opened by a user to load filament into the machine 180, and keptclosed otherwise. A compressible seal 234 is placed between the guideblock 214 and the canister body 216 to further seal the cassette 184.

[0071] The guide block 214 may carry an EEPROM 96 (described withrespect to embodiment one above). The circuit board 102 carrying EEPROM96 is mounted in a depression 262 of the guide block 214, with the pairof electrical contacts 106 facing out and the EEPROM 96 facing in. Thecircuit 102 is fastened to the guide block 214 by three screws 266. Forease of use, the guide block 214 preferably functions as a handle forthe cassette 184. In the embodiment shown, the guide block 214includes-a pair of grips 264 (shown in FIG. 14) on opposite sidesthereof.

[0072] The filament cassette 184 is assembled by placing the spool 186carrying the filament 188 on the hub 220 of the body 216, and feeding afilament strand into the guide block 214. The filament strand ispositioned along the filament path 236 so that it contacts the roller240. Optionally, packets of desiccant 62 (such as shown in regards toembodiment one) may be placed in compartments defined by spokes 225 ofthe spool 186. Then, the lid 218 is pressed onto the body 216, and thetape 223 is applied. It is then ready for use. The cassette 184 maylikewise be refilled and reused after the filament 188 that it containsbecomes depleted or unusable, by removing the lid 218 of the canister212 and replacing the filament 188 on the spool 186. When refilling acassette 184, the EEPROM 96 carried by circuit board 102 can be reset orthe circuit board replaced to provide a new EEPROM 96.

[0073] For moisture sensitive materials, the cassette 184 containing thespooled filament should be dried to a level at which the moisturecontent will not impair model quality. For most high-temperaturethermoplastics, for example polycarbonate, polyphenylsulfone,polycarbonate/ABS blend and Ultem™, an acceptable moisture content is alevel less than 700 parts per million (ppm) water content (as measuredusing the Karl Fischer method). Multiple techniques may be used to drythe filament.

[0074] The material may be dried by placing the cassette 184 containingspooled filament in an oven under vacuum conditions. The cassette 184 isplaced in the oven prior to attaching the circuit board 102 and prior toplugging the hole 226. The oven is set to a temperature suitable to thespecific modeling material type. For high-temperature thermoplastics, atemperature of between 175-220° F. is typical. The oven has a vacuumpump which maintains a dry environment in the oven. The hole 226 incanister 212 facilitates bringing the chamber of the canister 212 to theoven environment, so that the modeling material will be dried. When themoisture content of the material reaches a level desirable for themodeling material, the hole 226 is promptly sealed and the cassette 184removed from the oven. For high-temperature thermoplastics, an expecteddrying time is between 4-8 hours to reach less than 300 ppm watercontent. The circuit board 102 is then attached. The fully-assembledcassette 184 may be vacuum-sealed in a moisture-impermeable package,until its installation in a machine.

[0075] Alternatively, the packets of desiccant 62 alone may be used todry the material in the chamber of canister 212 without use of the oven.It has been demonstrated that placing packets 62 containingTri-Sorb-molecular sieve and calcium oxide (CaO) desiccant formulationsin the cassette 184 and sealing the cassette 184 in amoisture-impermeable package will dry the material to a water contentlevel of less than 700 ppm, and will dry the material to the preferredrange of 100-400 ppm. This desiccant-only drying method has advantagesover the oven-drying method in it requires no special equipment, and isfaster, cheaper and safer than oven drying. Suitable Tri-Sorb-molecularsieve desiccant formulations include the following: zeolite, NaA;zeolite, KA; zeolite, CaA; zeolite, NaX; and magnesium aluminosilicate.

[0076] Modeling filament in the cassette 184 can later be re-dried byoven-drying or by replacing the desiccant packets if the cassette 184becomes moisture contaminated while a usable amount of filament 188remains. Moisture contamination may occur, for example, if the accessdoor 250 is left open for a prolonged time period, if the cassette 184is removed from the machine 180 without replacing the plug cap 248, orit the cassette 184 is opened by a user.

[0077] The filament cassette receiver 190, which engages filamentcassette 184, is shown in detail in FIGS. 18 and 19. Each cassettereceiver 190 comprises a lift 270 and a drive block 272. As shown inFIG. 19, drive block 272 houses an entry conduit 274, an exit conduit276, a pair of rollers 278 and 279, a motor 280 and the latch 196.Roller 278 is a drive roller and roller 279 is an idler. The driveroller 278 is driven by the motor 280. The motor 280 is preferably a DCmotor with a current supply controlled by the controller 25. Motor 280extends laterally through the drive block 272 and couples to the driveroller 278 by a drive gear 282 attached to the shaft of the roller 278.

[0078] The exit conduit 276 is connected to the tubing 202. The filamentstrand provided from the guide block 214 passes through the entryconduit 274 to the rollers 278 and 279. The entry conduit 274 mates withthe exit orifice 238 of the guide block 214 when the cassette 184 isloaded and latched into modeling machine 180. To provide an airtightpath for the filament strand entering the drive block 272, a seal 284surrounds the entry conduit 274 near the entrance thereof, andcompresses against the guide block 214 of the loaded cassette 184. Fromthe rollers 278 and 279, the filament strand is provided to the exitconduit 276, and from there to the tubing 202. The tubing 202 makes anairtight seal with the exit conduit 276. Likewise, tubing 202 and tubing204 make an airtight seal with the ports 198 and 200 of the junctionblock 192, providing an airtight filament path from the cassette 184 tothe feed rollers 22.

[0079] The drive roller 278 and idler roller 279 must maintain gripping,frictional contact on the filament strand to advance it along thefilament path. To grip the filament strand, the rollers 278 and 279 maybe have elastomeric surfaces, or idler roller 279 may be spring-biasedtowards the drive roller 278, such as is described in U.S. Pat. No.5,121,329. An advantage of a spring-biased configuration is that theroller surfaces can be hard and more wear resistant. Preferably, thesurfaces of rollers 278 and 279 each also have a groove around thecircumference thereof to align the filament strand on its course fromthe entry conduit 274 to the exit conduit 276. The rollers 278 and 279are accessible to a user for maintenance through cover plate 308.

[0080] The drive block 272 also contains a filament sensor 286, which ispositioned along the filament path between the roller pair 278 and 279and the exit conduit 276. Sensor 286 is electrically connected to thecontroller 25, and provides a signal indicating whether or not filamentis present at the position of the sensor 286. In the exemplaryembodiment shown, the sensor is a floating axis microswitch sensor. Thedrive block 274 further carries an electrical connector 290. Theelectrical connector 290 has two pogo pins 142 that mate with theelectrical contacts 106 of circuit board 102, connecting the EEPROM 96carried by circuit board 102 to the controller 25. The EEPROM 96, whencontacted by the pogo pins 142, signals the controller 25 that thecassette 182 is present. In this manner, the machine 180 knows whetheror not each cassette 184 has been loaded.

[0081] The drive block 272 is manually raised and lowered by the use ofthe latch 196. The latch 196 has a handle 291 at one end thereof and alatch pin 292 at the other end thereof. The latch 196 extends throughthe drive block 272 such that the handle 291 is accessible to a user andthe latch pin 292 projects into a vertical slot 296 of the drive block272. The slot 296 receives a latch plate 294 which extends verticallydownward from the lift 270. The latch plate 294 has a hole 298 forreceiving the latch pin 292. Pulling on the handle 291 of the latch 196retracts the latch pin 292, allowing insertion and removal of the pin292 from the hole 298. When the latch pin 292 is inserted into the hole298, the drive block 272 is maintained in a raised position, allowingloading and unloading of the cassette 184 from the loading bay 182. Whenthe latch pin 292 is removed from the hole 298, the drive block 272drops to its lowered position where it engages the cassette 184 in theloading bay 182. A user manually raises or lowers the drive block 272 bygrabbing the latch handle 291, pulling forward, and either lifting orlowering the latch 196.

[0082] A pair of guide rods 302 are provided on the drive block 272,which couple the drive block 272 to the lift 270, and align the latchplate 294 in the slot 296. The guide rods 302 are mounted in tworeceptacles 288 on a top surface of the drive block 272. The guide rods302.extend vertically upward from the drive block 272 and through a pairof guide bearings 304 in the lift 270. A pair of e-clips 306 clip to theguide rods 302 above the lift 270 to support the drive block 272 in itslowered position. Preferably, a pair of springs 300 surround the guiderods 302 in the receptacles 272. In the raised position, the springs 300compress beneath the lift 270. When the latch 196 is pulled to removethe pin 292 from the hole 298, springs 302 force the drive block 272 toits lowered position.

[0083] The drying system 194 creates an active moisture barrier alongthe filament path, keeping the filament 188 dry while in the machine 18.In the exemplary embodiment, the drying system 194 is a dry-air purgesystem which provides dry air under pressure into air port 199 of thejunction blocks 192. The dry air flows through the tubing 204 and exitsthe tubing 204 near the liquifier 26. If the feed rollers 22 are used toadvance the filament strand into the liquifier 26, the filament willexit the tubing 204 as it enters the feed rollers 22. Alternatively, thefeed rollers 22 can be eliminated by using the roller pair 278 and 279in the drive block 272 to advance filament into the liquifier 26 at acontrolled rate. The exit of tubing 204 serves as a vent through whichany moisture that may have been trapped along the filament path isreleased. For instance, the air flow provided by drying system 194 willpurge any humid air that enters the drive block 272 during the time thatthe entry conduit 274 of the drive block 272 is not sealed to a filamentcassette 184. Additionally, the positive pressure maintained in thetubing 204 prevents humid air from entering the open end of the tubing204. By maintaining a positive pressure in the tubing 202 and 204 andpurging the filament path of any moisture, the drying system 194 allowsuse of the modeling machine 180 in a humid environment with moisturesensitive modeling material.

[0084] As mentioned above, the drying system 194 of the exemplaryembodiment comprises a compressor 206, a filter 208 and a regenerativedryer 210. The compressor 206 intakes ambient air and provides the airunder pressure to filter 208. Filter 208 removes water particles fromthe air. A Norgren™ F72G general purpose filter is suitable for thisapplication. From the filter 208, the air under pressure flows to thedryer 210, which is preferably a regenerative dryer, such as an MDHSeries dryer available from Twin Tower Engineering, Inc. of Broomfield,Colo. Dry air under pressure flows from the dryer 210 into each junctionblock 192. In alternative embodiments of the drying system, any sourceof dry air under pressure may be utilized successfully to purge moisturefrom the filament path, and other dry gases may be utilized as well.Importantly, the drying system should continuously feed dry air or othergas under pressure to the filament path, disallowing humid air fromremaining in or entering the filament path, and should be vented at ornear the end of the filament path. One alternative to drying system 194is to provide a compressed nitrogen tank as the dry gas source. Anotheralternative is a regenerative drying system, such as a hot air desiccantdryer having an output of less than or equal to about −40° F. dew point.

[0085] To install one of the cassettes 184 into the modeling machine180, the machine 180 is first turned on. The user then removes the plugcap 248 from the filament cassettes 184, and promptly inserts thecassette 184 into one of the loading bays 182. The plug cap 248 can beparked on the grooves 256 of the guide block 214, saving it for lateruse. The user latches the cassette 184 into place by pulling on latch196, as has been described. Once latched, the pogo pins 142 will contactthe circuit board 102, thereby connecting the EEPROM 96 to thecontroller 25. Once the controller 25 senses that the cassette 184 isloaded, the controller 25 will turn on the motor 280. The drive roller278 will then begin turning.

[0086] The user next opens the door 250 of the guide block 214 to accessthe roller 240, and manually turns roller 240 by exerting a downwardforce on the roller. The rotation of roller 240 will advance the strandof filament 188 out of the guide block 214 and into the entry conduit274 of the drive block 272. When the filament strand reaches the alreadyrotating drive roller 278, the roller pair 278 and 279 will grab thefilament strand and take over advancement of the strand from the user.The user promptly shuts the door 250 to seal the filament path. Theroller pair 278 and 279 then advance the filament strand at least as faras the position of the filament sensor 286. If the filament cassette 184is to be a standby cassette, the controller 25 will signal the motor 280to stop turning, so that advancement of the filament strand ceases atthe sensor 286. Alternatively, if the cassette 184 is to be a primarycassette, the roller pair 278 and 279 feed the filament strand throughthe junction block 192 to the feed rollers 22 (or alternatively to theliquifier 26). When the filament strand reaches the feed rollers 22, thefeed rollers 22 take over control of the filament strand advancement. Ifthe current on the motor 280 is set low enough and the filament is rigidenough, the motor 280 may be allowed to remain on and continue supplyinga constant push, but will stall out when the feed rollers 22 are not inmotion. This arrangement avoids having to turn the motor 280 on and offin synchrony with the operation of the feed rollers 22. In an alternateembodiment, the roller pair 278 and 279 may serve as the materialadvance mechanism in place of the feed rollers 22. In such a case, theoperation of motor 280 would be closely controlled by controller 25 tocontrol advancement filament into the extrusion head 20.

[0087] During modeling, the controller 25 can keep track of the amountof filament remaining in each cassette 184 by use of a count maintainedby each EEPROM 96. When one of the primary cassettes 184 becomesdepleted of filament, the modeling machine 180 will automatically switchto the standby cassette 184 without operator intervention. To unload thefilament, the controller drives the motor 24 backwards for a short timesufficient to pull the strand of filament 188 out of the liquifier 26and feed rollers 22. The controller 25 then drives the motor 280backwards to pull the filament strand out of the tubing 204, thejunction block 192, the tubing 202, and past the sensor 286. The machine180 knows that the junction block 192 is clear to receive filament fromthe standby cassette 184 when the sensor 286 of the primary cassettedrive block 272 indicates that filament is no longer present. Themachine 180 then loads filament from the standby cassette 184 to theextrusion head 20. This auto-unload/reload process is particularlybeneficial for modeling of large objects and when the modeling machine180 is operated beyond business hours. The user can replace the depletedcassette 184 while the machine 180 continues to build a model. Thedepleted cassette 184 can then be refilled and reused.

[0088] In the case that the user desires to remove one of the cassettes184 from the machine 180 before the cassette 184 is depleted offilament, the user may command the machine 180 to execute the unloadprocess. If a useable amount of filament 188 remains on cassette 184when it is removed from the modeling machine, the cassette 184 may bestored for later use without contamination. In such a case, the usershould seal the exit orifice 238 with the plug cap 248. If the cassette184 has a useable amount of filament 188 remaining but the filament hasbeen moisture contaminated, the cassette 184 may be re-dried asdescribed above.

[0089] As disclosed in U.S. Pat. No. 5,866,058, in building a model froma thermally solidifiable material, it is preferable to build the modelin a chamber heated to a temperature higher than the solidificationtemperature of the modeling material, and to cool the material graduallyfollowing deposition so as to relieve stresses from the material. Anumber of desireable thermoplastic modeling materials have high meltingpoints, for example, polycarbonate, polyphenylsulfone, polycarbonate/ABSblend and Ultem™, and additionally are moisture sensitive. A depositionmodeling apparatus which is particularly suitable for building models ata high temperature is disclosed in PCT Application No. US00/17363, whichhas been incorporated by reference herein. The modeling machine 180which uses a moisture-sealed material delivery apparatus according tothe second embodiment of the present invention may be an apparatus ofthe type that is a subject of PCT Application No. US00/17363, therebyproviding a dry, high temperature modeling environment. Varioushigh-temperature, moisture sensitive thermoplastics have beensuccessfully utilized in such a machine, namely, polycarbonate,polyphenylsulfone, polycarbonate/ABS blend and Ultem™ having a viscosityat the modeling temperature of less than 1200 Pa/sec at a shear rate of10 E⁻¹ sec⁻¹ and having a water content ranging between 100-400 ppm.These materials are stronger than ABS thermoplastic and have suitablethermal properties, melt viscosity, shrink characteristics and adhesionfor use in three-dimensional deposition modeling.

[0090] Although the present invention has been described with referenceto exemplary embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention. For example, the various features ofembodiment 1 may be used and interchanged with the features ofembodiment 2, and vice-versa. For example, the drying system ofembodiment 2 may be used with the design of embodiment 1, and embodiment1 may be used to provide primary and standby cassettes as disclosed withrespect to embodiment 2. Additionally, it will be apparent to those inthe art that the filament cassette and loading system of the presentinvention may be used to advantage in extrusion applications other thanthe building of three-dimensional models by a fused deposition process.Other changes may be made as well in keeping with the scope of theinvention. As an example, the motor for driving a roller carried by afilament cassette may be carried by the cassette rather than mounted onthe modeling machine. These and other changes will be apparent to oneskilled in the art.

1. An extrusion apparatus having a liquifier that receives a feedstockof material in filament form and delivers the material in a flowablestate, comprising: a loading bay; a substantially enclosed cassettecontaining spooled filament, inserted in the loading bay; and means forengaging a strand of the filament in the loading bay and advancing thefilament strand along a path to the liquifier.
 2. The extrusionapparatus of claim 1, and further comprising: a conduit having anentrance in the loading bay for guiding the filament strand as it isadvanced.
 3. The extrusion apparatus of claim 2, wherein the entrance ofthe conduit makes an airtight seal with an exit orifice of the cassette.4. The extrusion apparatus of claim 2, and further comprising:registration means for aligning the cassette with the conduit.
 5. Athree-dimensional modeling machine having a liquifier that receivesmodeling material in filament form and delivers the material in aflowable state, comprising: a loading bay for receiving a cassettecontaining spooled filament; means for engaging a strand of the filamentin the loading bay; and means for automatically advancing the filamentstrand along a path to the liquifier.
 6. The three-dimensional modelingmachine of claim 5, and further comprising: a conduit having an entrancein the loading bay for guiding the filament strand as it is advanced. 7.The three-dimensional modeling machine of claim 5, and furthercomprising: registration means for aligning the cassette with theconduit.
 8. The three-dimensional modeling machine of claim 5, andfurther comprising: latching means for engaging and disengaging thecassette in the loading bay.
 9. The three-dimensional modeling machineof claim 5, and further comprising: means for ejecting the cassette fromthe loading bay.
 10. A three-dimensional modeling machine having aliquifier that receives modeling material in filament form and deliversthe material in a flowable state, comprising: a loading bay forreceiving a cassette containing spooled filament; and a filamentcassette receiver for engaging the cassette in the loading bay, saidreceiver comprising: a conduit for receiving a filament strand from thecassette and guiding the filament strand along a path to the liquifier;and means for advancing the filament strand through the conduit.
 11. Thethree-dimensional modeling machine of claim 10, wherein the means foradvancing comprises: a pair of feed rollers having a nip therebetweenfor receiving the filament strand; and a drive mechanism coupled to thefeed rollers.
 12. The three-dimensional modeling machine of claim 11,wherein the feed rollers are in the conduit.
 13. The three-dimensionalmodeling machine of claim 10, wherein the means for advancing comprises:a drive wheel configured to mate with a follower wheel on the cassette;and a drive mechanism coupled to the drive wheel.
 14. Thethree-dimensional modeling machine of claim 13, wherein the filamentcassette receiver further comprises: a drive engagement means forengaging and disengaging the drive wheel.
 15. The three-dimensionalmodeling machine of claim 10, and further comprising: a sensor fordetecting presence of the filament strand at a sensing position of thepath approaching the liquifier; wherein the means for advancing isdisabled in response to a detection indication provided by the sensor.16. The three-dimensional modeling machine of claim 15, and furthercomprising: a pair of feed rollers located proximate the sensingposition.
 17. The three-dimensional modeling machine of claim 10,wherein the filament cassette receiver further comprises: registrationmeans for aligning an exit orifice of the cassette with an entrance ofthe conduit.
 18. The three-dimensional modeling machine of claim 10,wherein an entrance of the conduit is configured to make an airtightseal with an exit orifice of the cassette.
 19. A three-dimensionalmodeling machine having a liquifier that receives modeling material infilament form and delivers the material in a flowable state, comprising:a loading bay for receiving a cassette containing spooled filament; aconduit configured to mate with an exit orifice of the cassette forreceiving a filament strand from the cassette and guiding the filamentstrand along a path to the liquifier; and a drive roller for advancingthe filament strand through the conduit.
 20. The three-dimensionalmodeling machine of claim 19, and further comprising: a latch forengaging and disengaging the cassette in the loading bay.
 21. Thethree-dimensional modeling machine of claim 19, wherein the entrance ofthe conduit makes an airtight seal with an exit orifice of the cassette.22. The three-dimensional modeling machine of claim 19, and furthercomprising: registration means for aligning the cassette with theconduit.
 23. The three-dimensional modeling machine of claim 19, andfurther comprising: means for ejecting the cassette from the loadingbay.
 24. The three-dimensional modeling machine of claim 19, and furthercomprising: a follower roller positioned opposite the drive roller. 25.The three-dimensional modeling machine of claim 24, wherein the driveroller and the follower roller are in the conduit.
 26. Thethree-dimensional modeling machine of claim 19, wherein the drive rolleris a wheel configured to engage a follower wheel on the cassette. 27.The extrusion apparatus of claim 26, and further comprising: driveengagement means for engaging and disengaging the drive roller from thecassette.
 28. The extrusion apparatus of claim 27, and furthercomprising: a pair of feed rollers positioned along the path proximatethe liquifier; and a sensor for detecting presence of the filamentstrand between the feed rollers and providing a detection indication;wherein the drive engagement means disengages the drive roller inresponse to the detection indication.